[cdc_rsync] Move sockets to common (#95)

There are no real changes, just moving files around. Sockets will be
used in the future to find available ports in cdc_stream. Therefore,
they need to be in common.

common/client_socket.h

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef COMMON_CLIENT_SOCKET_H_
+#define COMMON_CLIENT_SOCKET_H_
+
+#include <memory>
+
+#include "absl/status/status.h"
+#include "common/socket.h"
+
+namespace cdc_ft {
+
+class ClientSocket : public Socket {
+ public:
+  ClientSocket();
+  ~ClientSocket();
+
+  // Connects to localhost on |port|.
+  absl::Status Connect(int port);
+
+  // Disconnects again. No-op if not connected.
+  void Disconnect();
+
+  // Shuts down the sending end of the socket. This will interrupt any receive
+  // calls on the server and shut it down.
+  absl::Status ShutdownSendingEnd();
+
+  // Socket:
+  absl::Status Send(const void* buffer, size_t size) override;
+  absl::Status Receive(void* buffer, size_t size, bool allow_partial_read,
+                       size_t* bytes_received) override;
+
+ private:
+  std::unique_ptr<struct ClientSocketInfo> socket_info_;
+};
+
+}  // namespace cdc_ft
+
+#endif  // COMMON_CLIENT_SOCKET_H_